1. Field of the Invention
This invention relates to particle beam systems used in the manufacture of microminiature devices (integrated circuits) and is particularly directed to a new and improved writing technique (process) for a particle beam lithography system and the primary object of this invention is to provide a means of changing the dimension of lines written by existing lithographic systems without major software changes in such systems.
2. Prior Art
Lithographic systems using a controllable electron beam, sometimes called E-beam machines, for the fabrication of integrated circuits are old in the art; one such system is described at length in the U.S. Pat. No. 3,900,737 to Collier et al. and another in the U.S. Pat. 3,801,792 to Lin.
In these patented machines, a medium of resist material upon which the electron beam is to perform its writing operation is positioned on a motor driven stage which is moved continuously and in synchronism as the beam is scanned in a raster fashion in a direction perpendicular to the stage motion. In practice, the diameter of the round electron beam spot, also called a "gaussian spot" or "pixel", focused on the resist layer, is also the "address" dimension of the system. Typically, at least four rows of addresses (pixels) in the stage travel direction define the width of a "feature" and the length of the feature is formed by a number of pixels in the raster scan direction. The pattern on the resist defined by the beam and by the stage movement is determined by the system control equipment and software therefor.
In some cases, it has been found to be desirable to write a line with a change in feature width or length by an amount which is not an integral multiple of the selected pixel size. Suppose, for example, one wanted to write a feature of a width equal to 41/2 pixel diameters. The prior art would require a reduction in pixel size and an increase in the number of raster scans. The pixel size would be reduced by 1/2 in order to change the feature width by one-half a pixel. The number of scans in the feature direction must then be increased. Using the smaller pixel size would require 9 scans to produce the desired feature width (eight scans to obtain the width equal to four rows of the larger pixel plus one scan for the desired 1/2 pixel increase in feature width). This example of decreased pixel size can be stated another way, i.e. the throughput of a raster scan E-beam lithographic system is inversely proportional to the square of the pixel size. It can be appreciated that the lesser pixel size to provide the wider line width in the feature direction is undesirable since it reduces the throughput of the machine dramatically. It should be clear also that to increase the feature length by less than one width of a large pixel would present the same problem as the above described increase in feature width. This invention shows that the feature width or length can be changed by less than 1 pixel diameter without changing the pixel size, thus keeping the throughput of the machine unchanged.